Several DNA constructs or vectors, which are suitable for the expression of proteins, which are encoded by sequences within such a DNA construct, are known in the state of the art. Depending on the organism or cell type into which an expression construct should be introduced they are designated as eukaryotic or prokaryotic expression constructs. The term “plasmid” is commonly related to circular expression constructs comprising a covalently closed circular DNA double-strand. Plasmids usually contain further sequences in addition to the ones, which should be expressed, like marker genes for their specific selection and in some cases sequences for their episomal replication in a target cell.
A structurally different expression construct is described in the EP 0 941 318. This document discloses a dumbbell-shaped linear, covalently closed DNA construct with partially single stranded loops at both ends. Such a construct causes after transfection significantly increased levels of protein expression, depending on the method for introducing the DNA construct into the cell.
The EP 0 941 318 discloses further that it is advantageously with regard to the protein expression to apply such a dumbbell-shaped DNA constructs via ballistic transfer. Although the expression level increases, it is laborious to link the DNA by means of absorption, covalently or ionic binding to the micro projectiles which are used for the ballistic transfer.
Jet injectors, which are appropriate for DNA transfer into a cell, are known in the state of the art, e.g. for the application of vaccines. Such a jet injector is usually a medical device with an injecting syringe, which uses a high-pressure narrow jet for the injection of liquids. The difference to usually used hypodermic needles to penetrate the epidermis is that a jet injector reduces the pain associated with the corresponding injection. Commonly, a jet injector is powered by compressed air or gas, either by a pressure hose from a large cylinder or from a built in gas cartridge or small cylinder. Basically, jet injectors are used as alternatives to needle syringes.